I'll agree with altenbach, but add a quick and dirty solution is to just put the installer in a password protected, self-extracting ZIP file. It's not a terribly robust solution since anyone with the password could just unzip it and distribute it, but if you're just looking for a deterrent, that might be sufficient.
altenbach suggests the preferred alternative here: http://forums.ni.com/t5/LabVIEW-Idea-Exchange/Protect-Installer-with-password/idc-p/3194329#M32468